Evaluating the invasiveness of Acacia paradoxa in South Africa

We present the first detailed survey of a population of Acacia paradoxa DC. (syn. Acacia armata R.Br.), Kangaroo Thorn, in South Africa. The species is listed under the Conservation of Agricultural Resources Act as a category I invasive plant and, until 2008, was being managed as part of Working for Water's general alien clearing operations. Acacia paradoxa is currently restricted to a small population (similar to 11,350 plants over similar to 295 ha) on the northern slopes of Devil's Peak, Table Mountain National Park in the Western Cape. Its distribution is highly clumped, and at a local scale it has formed thick stands of up to 20 plants m(-2). Using a bioclimatic model we predict that it has a large potential distribution in South Africa, especially along the southern coast. We confirmed the categorisation of A. paradoxa as a potential landscape transformer that requires immediate control by conducting a formal risk assessment using the Australian Weed Risk Assessment system. However, the population appears to be spreading slowly, and, while there is a significant seed-bank in some places (similar to 1000 seeds m(-2)), this is largely restricted to below the canopy of existing plants. Therefore, the population has not and likely will not rapidly spread in area, and so containment is feasible. Dedicated and thorough annual follow ups are required because plants can produce seeds when they are I year old and standard clearing operations have missed flowering plants. (C) 2009 SAAB. Published by Elsevier B.V. All rights reserved.